1. Technical Field
This invention relates to an on-vehicle fault detecting device that can detect an abnormality when data, such as wireless operation history of a mobile device and vehicle specification information, is written in or read from a memory.
2. Related Art
An on-vehicle fault detecting device as disclosed in Japanese Patent Application Publication No. 2002-24101 includes a power source IC, a main microcomputer, a sub-microcomputer, and an EEPROM (a nonvolatile memory). The power source IC is operative to output a reset signal to the main microcomputer when the power supply voltage drops below a predetermined reset voltage. Data is written in the EEPROM by the sub-microcomputer. In an ECU, a bottom operating voltage of the main microcomputer is set to be below the reset voltage, and a bottom operating voltage of the sub-microcomputer is set to be above the reset voltage. When the power supply voltage drops to the bottom operating voltage of the sub-microcomputer, the main microcomputer prohibits the sub-microcomputer from writing data in the EEPROM. This can prevent the sub-microcomputer from writing erroneous data in the EEPROM. Such erroneous writing is likely to occur when the power supply voltage drops to the bottom operating voltage of the sub-microcomputer.
Known on-vehicle fault detecting devices, including the device as disclosed in Japanese Patent Application Publication No. 2002-24101, prevent data different from intended-to-be-written data from being written in a nonvolatile memory (a storage unit), by means of well-known checking techniques, such as a parity-bit check, a checksum, an error-correcting code check, and verification.
Whereas, despite using the known techniques, it may not be ensured that the intended data is correctly written in the memory. In other words, data different from the intended data may be erroneously written in the memory.
As a solution to such a deficiency, there is known an on-vehicle fault detecting device that writes data in a memory, then reads the written data from the memory, and determines whether or not the read data is coincident with data intended to be written in the memory. In cases where it is determined that the read data is not coincident with the intended data, the data is again written in the memory. The fault detecting device counts a number of times that it is continuously (or consecutively) determined that the read data is not coincident with the intended data, and in cases where the number of times of continuous non-coincidence has reached a predetermined determination number of times of continuous non-coincidence (for example, two times), it will be written in the memory that there has occurred a fault in hardware or that there exists a fault in hardware.
This enables a user, such as maintenance personnel, to detect a fault in hardware (or a fault in a hardware component, such as EEPROM) itself by reading the occurrence of a fault in hardware from the memory through a dedicated tool. It should be noted, however, that the occurrence of a fault in hardware may fail to be written in the memory. In such cases, it is difficult to detect a hardware fault because of lack of the occurrence of a fault in hardware in the memory.
Even in cases where the number of times of continuous non-coincidence has reached the predetermined determination number, there may be cases where it cannot be concluded that there has occurred a hardware fault. Therefore, the on-vehicle fault detecting device may be configured to take appropriate control measures, such as outputting the occurrence of a fault in hardware directly to the dedicated tool or preventing the read data from being used, instead of writing the occurrence of a fault in hardware in the memory.
What causes data different from the intended data to be erroneously written in the memory may be considered to be not only a continuous abnormality, such as a fault in hardware (e.g., EEPROM) itself, but also a temporary abnormality that results from a usage environment around a vehicle equipped with the fault detecting device, such as an environment rich in strong radio waves emitted from a manufacturing facility or a transformer station or other sources.
The above known on-vehicle fault detecting devices are only operative to determine that there is a an abnormality in data in cases where the number of times of continuous non-coincidence has reached the determination number, and are not capable of identifying what has caused data different from intended data to be written in the memory. Therefore, even if a true cause of the fault is a usage environment around the vehicle, there will be written in the memory that there has occurred (or exists) a fault in the on-vehicle fault detecting device itself or in its hardware (EEPROM) itself, which will lead to an erroneous judgment.
It should be noted that such a situation may occur not only in writing data in a memory but also in reading written data from a memory.